This book explores the human right to leave any country – including one's own – in international law, and its applicability to externalised migration control. It develops a framework for interpreting the right and demonstrates how various externalisation measures violate it, leading to the international responsibility of states and international organisations. Analysing the work of international and regional systems enshrining the right and examining global externalisation practices, it demonstrates the radical reform required by states and international organisations to comply with the right to leave. Implementing the author's recommendations would compel the dismantlement of many current externalisation strategies and a re-imagining of the global (im)mobility regime. This book offers compelling insights for lawyers in the fields of international law, human rights and refugee law, as well as migration policymakers, practitioners and officials.